Method for drawing small diameter wires



July 4, 1939. P. R. KALISCHER 2,165,056

METHOD FOR DRAWING SMALL DIAMETER WIRES Filed Nov. 27, 1957 WITNESSES: I INVENTOR 5 WM Philip/P. alz'scher Patented July 4, 1939 UNITED STATES PATENT OFFICE METHOD FOR DRAWING SMALL DIAIHETER WIRES Philip R. Kalischer, Wilkinsburg,,Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 21, 1931, Serial No. 176,853

panles, it is not feasible to prepare tin wire hav-' ing a smaller diameter than 33 mils since the natural and obvious limitations of the extrusion process prohibit further reduction while the tensile strength of tin is so low as to prohibit drawing the wire to a smaller size.

An object ,of this invention is the provision of ,a process whereby small diameter wire may be drawn from tin.

Another object of this invention is the provision of a process in which the tensile strength of tin is so increased-as to permit it to be drawn 30 into a small diameter wire.

Other objects ofthis invention will become apparent from the following description when taken in conjunction with the accompanying drawing, the single figure of which is a plan view partly in section of the apparatus employed in practicing this invention. Referring to the drawing, this invention islllustrated with reference to a drawing apparatus Ill. The drawing apparatus comprises the usual die block I! and a diamond die l4 suitably car-'- ried therein and a coolant chamber l6 associated in intimate relation therewith. The coolant chamber l6 and the cavity l8 in the die block adjacent the diamond die I! are disposed to retain a supply of solid carbon dioxide or dry ice 20, the purpose of which will be explained here-,

inafter, and are provided with a removable cover 22and an opening Ifrespectively, for replenishing the supply of dry ice. Associated with the coolant chamber l6 and the drawing die M are wire reels 26 and 28, respectively, the reel 26 functioning to carry thewire 30 to be drawn while the reel 28 functions as a pulling reel to exert suflicient force to draw the wire through the cooled reducing die. In the illustration, the pulling reel 28 is disposed as close as possible to the die block, the reason for which will be ex plained hereinafter.

1 In drawing wire to a smaller diameter, the force exerted by the pulling reel mustbe greater than the sum of the forces resisting the change in size of the wire or greater than the sum of the friction between the wire and the drawing die and the resistance of the metal to plastic de- 66 formation. The tensile strength of tin which recrystallizes at about room temperature or about 20= C. is insuflicient to withstand the pulling force exerted in drawing the wire at ordinary temperatures.

In practicing this invention, the wire to be 5 drawn is cooled to a' temperature ranging between 10 C. and +10 C. and preferably between 5 C. and +5 C. to increase its hardness. Since the tensile strength of a metal increases in a substantially linear relation with an in- 10 crease in hardness, it is found that in the cooled condition, the tensile strength of tin is sufficient to withstand the pullingi force exerted in eflecting a reduction in the size of the wire. In cooling the wire, 'care must be exercised that the is temperature of the wire is not lowered too much or a brittle stage is reached where it is impossible to draw the wire. In practice, the temperature range given'hereinbefore and particu larly 0 C. is found to be satisfactory for imgo parting an increase in the tensile strength without embrittling the metal.

As illustrated in the drawing, the cavity IS in the die block and the coolant chamber it are filled-with small pieces of solid carbon dioxide 25 and the wire to be drawn into a smaller diameter ispasse from the supply reel 26 through the solid carbon dioxide inthe coolant chamber and the cavity through the die I4, and thence to the pulling reel 28. By maintaining the supply of 80 solid carbon dioxide adjacent the die M, the temperature of the die approximates the temperature of the wire in the coolant chamber l6.

The temperature of the die may be measured by any suitable means such as a thermocouple or a 35 thermometer. The cooling of the die is necessary in order to dissipate the heat evolved during the drawing operation, thereby preventing an annealing and softening of the metal.

Since the tensile strength of the tin-wire decreases as the temperature of the wire increases to room temperature, it is necessary to relieve the tension or remove the pulling or drawing force before the tensile strength of the drawn wire decreases to the breakingpoint of the wire. In order to prevent such a breaking of the wire, the pulling reel 28 is disposed asclose to the die block I! as is possible to permit the winding of the reduced wire while in the cooled condition. 50 Where it is impossible to position the winding reel 28 adjacent the die block, as illustrated, another coolant chamber, notshown, filled with dry ice to maintain the drawn wire at a low temperature may be disposed adjacent the die block between the die block and the pulling reel with the pulling reel adjacent the coolant chamber.

In drawing the wire, care must be exercised in controlling the speed of drawing through the die and the reduction-per pass as well as the temperature of the wire and of the die. Ifv the drawing rate is too fast or the reduction per pass too large, heat is generated in the wire and in the die at too fast a rate to be dissipated bythe cooled dieand die block, with the result that the temperature of the die increases and the wire drawn from the die is tooryvarm to have the necessary tensile strength to withstand the pulling force. In practice, it is found that with the wire and die cooled to between -'-5 C. and'+5 C. and preferably to 0 (2., that a safe drawing. rate ranges from between 50 and 150 feetper minute for a reduction of between .2 to 4 mils per pass, depending upon the size of, the wire being reduced,

In a process developed for a quick reduction of extruded tin wire from an extruded size of not less than 33 mils in diameter to a small diameter of vl0 mils, the extruded wire is passed through the coolant chamber where it is cooled to about 0 C. and thence through the'reducing die ll which is maintained at a C. at a drawing rate of not more than 150 feet per minute with a reduction of not more than 4 mils, after which it is wound on the pulling reel disposed adjacent the die block. The empty supply reel and "the fullpulling reel are then interchanged and the drawing operation is repeated a number of ,times, pulling the wire through the coolant chamber and the cooled die until a diameter of about 20 mils is obtained. The drawing rate of 150 feet per minute and the reduction of 4 mils per pass are the maximum values suitable for use, since greater speeds and greater reductions so heat'the wire that the heat cannot be dissipated by the cooled die and the heated wire breaks under the force exerted by the pulling reel.

After a size of 20 mils is obtained, the diameter of the wire is further reduced by further passing the wire through the coolant chamber and the cooled reducing die at a drawing rate of about 100 feet per minute with a reduction of not more than 1 mil per pass a s'uificient number of times to secure a diameter of about'15mils. For wire ranging in size from 15 mils to 20 mils, it is found that the maximum permissible drawing rate is 100 feet per minute with a maximum permissible reduction of one mil per pass. If either of these values are substantially increased, the heat developed cannot be dissipated anithe wire may break as it is drawn from the cooled die.

In order to further reduce the tin wire, it is necessary to further lower the drawing rate to not more than 60 feet per minute with a reduction of not more than .4 of a mil per pass. By employingthese values and repeatedly passing the wire through the coolant chamber and the cooled reducing die, the wire may be reduced to a diameter of about 10 mils.

By practicing the process described hereinbefore, an extremely fine wire suitable for use as fuse wire may be produced. A wire thus produced has a very uniform cross section.

Although in the specific embodiment disclosed, a process is described for drawing wire into 10 mil size, it is, of course, to be understood that where a size ranging between the extruded size and I the 10 mil size is desired, the process may be stopped when the wire reaches the desired reduced size. The 'wire can also be drawn to less temperature-of about 0 than the 10 n size by s'uitably adjusting thev reduction per pass and the drawing rate. Further, in the process and apparatus described, solid ployed as long as the temperatureof "th'ecoolant,

chamber and the cooling die is controlled within the range given and the cooling -medium does not give ofi deleterious liquids or gases which will adversely affect the tin.

' Although this invention has been described with reference to a particular embodiment thereof, it is, of course, not to be limited thereto except insofar as is necessitated by the prior art.

and the scope of the appended claims. I claimras my invention:

1. A process for drawing small diameter wire from tin comprising, extruding tin into wire of predetermined size, cooling the extruded wire to a temperature ranging from about-5.C. ,to about 5 c. to increase its tensile.strength,;c 0 i reducing die to a temperature approximatingthe temperature of the cooled extruded wire,-and

drawing the cooled extruded wire through the 2..A process for drawing small diameter cooled die to. effect a reduction in size and pro- 'duce a small diameter, wire. 5

from tin comprisingeXtrtiding tin into wire of temperature rangingfromabout -5* C. to 5". C.

, to increase its tensile strength, cooling a reducing predetermined cooling the extrudedwire to a I the reducing die to prevent a substantial decrease in the tensile strength of...the wire as it is withdrawn from the die.

3. A process for drawing small diameter wire from tin, comprising, extruding tin into wire of predetermined size, cooling the extruded wire to a temperature ranging from 5 C. to 5 C. toincrease its tensile strength, cooling a reducing die to a temperature approximating the temperature of the cooled extruded wire, and drawing the cooled extruded wire through the cooled'die at a drawing rate of from about 60 to l50'feet per minute to reduce the wire from .2' m4 mils per pass.

4. A process according to claim 3 wherein the steps of cooling the wire and die and drawing the cooled wire are repeated toeffect e reduction of the wire to a predetermined size.

,5.'A process for drawing small diameter wire from tin, comprising, extruding tin into wire of not less than 33 mils in diameter, cooling the ex: truded wire to a temperature ranging from 5 to 5 C. to increase its tensile strength,'cooling a reducing die to a temperature approximating the temperature of the cooled extruded wire, drawing the cooled extruded wire through the cooled die at a drawing rate of-about 150 feet per minute ,to reduce the wire not more than 4 mils per pass,

repeating the drawing at a reduction of not more than 4 mils per passuntil a. diameter of about 20 mils is obtained, further. drawing the cooled wire through the cooled die at a drawing rate of about feet per minute with a reduction of "not more than 1 mil per pass until a diameter of about 15 mils is'obtained, and then continuing'the drawing of the cooled wire through the cooled die at a drawing rate of about 60 ieet'per minute with a reduction of not more than .4 of a mil per pass until a diameter of about 10 mils is obtained.

6. A process according to claim 3 wherein the wire is cooled by passing it through solid carbon dioxide so disposed as to contact the reducing die to cool it. v I

'7. A process for drawing small diameter wire from tin, comprising, extruding tin into wire of not less than 33 mils in diameter, cooling the extruded wire to a temperature ranging from -5 C. to 5 C. to increase its tensile strength, cooling a reducing die to a temperature approximating the temperature of the cooled extrudedwire, drawing the cooled extruded wire through the cooled die at a drawing rate of from about 60 to about 150 feet per minute to reduce the wire from .2 mil to 4 mils per pass, and winding the drawn wire .on a reel before the wire under tension between the reducing die and the reel becomes so warm as to have its tensile strength lowered to the breaking point of the wire.

8. A process for drawing small diameter wire from tin, comprising, extruding tin into wire of not less than 33 mils in diameter, cooling the extruded wire to a temperature ranging from 5 C. to 5 C. to increase its tensile strength, cooling a reducing die to a temperature approximating the temperature of the cooled extruded wire, drawing the cooled extruded wire through the cooled die at a drawing rate of about 150 feet per minute to reduce the wire not more than 4 mils per pass, repeating the drawing at a reduction of not more than 4 mils per pass until a diameter of about 20 mils is obtained, further drawing the cooled wire through the cooled die at a drawing rate of about 100 feet per minute with a reduction of not more than 1 mil per pass until a diameter of about 15 mils is obtained, and then continuing the drawing of the cooled wire through the cooled die at a drawing rate of about 60 feet per minute with a reduction of not more than .4 of a. mil per pass until a diameter of about 10 mils is obtained, and winding the drawn wire on a reel before the wire under tension between the reducing die and the reel becomes so warm as to have its tensile strength lowered to the breaking point of the wire.

9. A process according to claim 5 wherein the drawn wire is wound on a reel after each drawing operation before the wire under tension between the reducing die and the reel becomes so warm as to have its tensile strength lowered to the breaking point of the wire, the wire and die being cooled before each succeeding drawing to reduce the size of the wire.

PHILIP R. KALISCHER. 

